[Samsung Galaxy Nexus] cmoG530:
Via AndroidPolice

"The numbers and the videos together paint a picture of where ART stands today. It will definitely make a difference, but its current incarnation just hasn't matured enough to deliver significant gains. Floating-point calculations and basic responsiveness are obviously reaping the benefits of the new runtime, but that's about it. There's little or no overall improvement for integer calculations, most regular code execution, or much of anything else. In fact, it looks like gamers would be better served by sticking to Dalvik, for now.

Why aren't the benchmarks blowing us away? If I were to make a guess, it's probably because the first goal in developing ART was to make sure it was functional and stable before the heavy optimizations came into effect. If that's the case, there is probably quite a bit of code for error-checking and logging just to ensure everything is operating as it should, which might even be responsible for more overhead than we had with Dalvik. Even in the places where ART doesn't outperform Dalvik, the numbers tend to remain reasonably close. As subsequent versions of the runtime emerge from Mountain View, we should expect to see the performance gap growing wider as ART pulls ahead.

Now for the real question: is it worth switching to ART right now? Google obviously isn't recommending it for regular users, and I tend to agree. While ART seems very solid and I feel like responsiveness is better - possibly just the placebo effect - there are still circumstances where it is unstable and causes apps to crash. If there is even a single instance where you have to switch back to Dalvik to get an app to run correctly, that inconvenience far outweighs the minimal performance gain you might have had. Once I've finished this series, I will probably stick to Dalvik for the remainder of KitKat; and I imagine most people will be better served by doing the same.”

"I expect the majority of the people claiming wildly better battery life are experiencing a placebo effect. After all, every test I ran demonstrated no more than about 2%-4% difference after burning through nearly 50% of the battery.

Still, I'm fairly certain early adopters won’t be swayed to return to Dalvik, and I'm not really sure they should be. If you’re on the fence about switching, I would still advise sticking to Dalvik, at least until the next version of Android. Aside from smoother animations and scrolling, this version certainly doesn’t offer any profound increase in performance or battery life, and it’s still prone to occasional bugs. At this stage, it’s still something best left to developers and some enthusiasts.

It’s important to remember that these underwhelming results are coming from a preview version of software the Android Team did not intend for regular users to even start using yet. The code isn’t optimized to the extent that we know it can be, and there are surely several safety checks to guard against bugs, all of which are adding overhead that will eventually become unnecessary. Of course, nobody wants ART to land in the crosshairs of an upcoming Bug Watch (wink), so let’s not be too hasty about stripping out those safety measures. Nonetheless, the current incarnation is simply about getting everything working and introducing a new runtime to the world. We should be looking forward to future versions for more tangible improvements."